1. Field of the Invention
The present invention generally relates to a rotating support apparatus in a disk storage device, such as a magnetic disk device or an optical disk device, and more particularly, relates to a spindle assembly or a magnetic head positioner, in a disk file apparatus used as an external storage device of a computer.
2. Description of the Related Art
FIG. 6 shows a conventional spindle assembly in a disk file apparatus, in which shaft 1 is secured at opposite ends thereof to a disk housing (not shown) and is fitted with a pair of ball bearings 2 and 2', which are spaced from one another at a predetermined distance along the axis of the shaft 1. The outer races 2b of the ball bearings 2 and 2' are fitted in a hub 3, which supports a plurality of superimposed magnetic disks 4. An internal space 5 of the spindle hub 3 is provided with a larger diameter, to enable a motor (not shown) to be accommodated therein to drive (rotate) the magnetic disks 5. The lower bearing 2' is fitted in the internal space 5 though a ring (spacer) 6 having a uniform outer diameter.
In a known spindle arrangement as shown in FIG. 6, the upper ball bearing 2 (which is usually made of iron or the like) is directly fitted in the inner surface of the hub 3 (which is usually made of aluminium or the like), and the lower ball bearing 2' is fitted in the inner surface of the hub 3 through the ring 6 (which is usually made of steel, aluminium or the like), as mentioned above, and since there is a difference in the coefficients of linear expansion of the materials of the ball bearing 2 (iron) and the hub 3 (aluminium), and of the ring 6 (iron) and the hub 3 (aluminium), 1 a thermal off-tracking and 2 a thermal decentering of the rotating apparatus, including the magnetic disks 4, may occur due to changes in the temperature. Namely, in the thermal off-tracking, a thermal deformation on the order of microns takes place at the outer peripheral surface of the hub and the magnetic disk supporting surfaces of the hub 3, resulting in a thermal deformation of the superimposed magnetic disks into an umbrella shape or a deviation thereof. In the thermal decentering of the rotating apparatus, the center of rotation of the rotating apparatus is deviated due to a gap produced between the hub 3 and the ball bearing 2 or the ring 6, which results in a failure to precisely and correctly read and write signal information from and to the magnetic disks 4.